The tradition of a marathon being 26.2 miles long began in 1908 when the Olympics was held in London, England. Queen Alexandra asked that the race start on the Windsor Castle lawn so that the children in the nursery could watch from their window, and that the race's end be in front of the royal box.
The route, which measured 26.2 miles, stuck. In 1921, the official standard for a marathon was set at 26.2 miles and is the standard as of 2015. Previously, the length of a marathon was set at 40 kilometers, which is nearly 25 miles. The ancient Greek games did not involve lengthy foot races.